The present invention refers to a convergent multibeam unit for radiation and particularly to a combination of lineal accelerator with stereotaxic means that contribute with substantial advantages to the devices used at present for radiation of the cerebral structures.
Stereotaxy, which was initiated at beginning of this century with a Horsley and Clark device used on animals for experimentation, made it possible to locate different intracerebral structures with precision and to reach said structures with stimulation and coagulation electrodes; it was developed until 1947, when Spiegel and Wycis reported in the U.S.A. the first concept of a stereotaxic device adapted for human use. Subsequently, different reports were made from scientific societies of several European countries.
In France, Prof. Jean Talairach was the pioneer of this discipline; his contribution constitutes the most important neurosurgical work of that country.
At present the possibility of observing the course of the encephalic vessels in each individual case makes it possible to locate the cerebral fissures and convolutions with precision, and consequently, effect multiple biopsies. From an exact diagnosis and the consequent histoprognosis an adequate therapy can be selected.
The possibilities of treatment would be:
(a) Surgical ablation (total or partial) if a situation and extent of injury allows it, PA1 (b) Radioactive interstitial implantation (with Iridium 192 or Iodine 125), PA1 (c) External radiation with lineal accelerator due to its penetration and minor effect on the skin compared, for example, with Cobalt 60, PA1 (d) Radiation with Cobalt 60 with multiple fixed sources ("Gamma Unit"), to which reference shall be made below and, finally; PA1 (e) Radiation with the convergent multibeam unit of the invention in stereotaxic condition.
Of the radiation methods in which we are interested, implantation is effected on small glia tumors of low malignant degree and situated in the nervous parenchyma.
Radiation through teletherapy with a lineal accelerator is used only on extensive tumors, or in protocols of "implantation-teletherapy with lineal accelerator" association, placing an important tumoricide dose on the tumor itself and a smaller dose on the periphery of same to destroy the tumor cells that are at a distance from the center of the injury and that can be responsible for its reappearance.
The application of the convergent multibeam unit of the invention is based on the necessity to apply a high dose in the center of the tumor, with a rapid decrease of the dose on the edges and the possibility of protecting the normal operational structures that have not been infiltrated by a tumor, without applying too small a dose on the latter.
Numerous working trials have demonstrated that, as the volume of radiation is increased, either through teletherapy or interstitial, the possibilities of radionecrosis are consequently increased. This means the death of the tumor in a significant of cases, but the complications to which this leads also cause the death of the patient. Over and above a volume of approximately 5.times.5.times.5 cm a radionecrosis is mortal notwithstanding its surgical extirpation (which is sometimes possible), due to complications of uncontrollable edema. Experience with biopsies and necropsies corroborates this.
If at the same time the precision of the methodology permits examination of the exact limits of the injury, the ideal would be to apply a therapy that, without losing its efficiency, must be as circumscribed as possible, reducing its diameter. This implies the necessity of a strict localization, obtainable by means of estereotaxy and a minimum of the complications based on the reduction of the diameter of the radiation beams and the multiplication in number of the entries that allow to obtain, within the perfectly admissible tolerances for each of them, the concentration on the area, in this case the tumor, of the sum of said radiations.
The focal concentration of numberless radiation beams of high energy (6 to 12 MV) centered on the injury obtain the desired end.
The smallest fields used in teletherapy for the axion are of 4.times.4 cm. If, as stated above, radionecrosis is the inevitable result of radiation on volumes of the order of 5.times.5.times.5 cm, the danger limits become very narrow.